This invention relates to a method for fabricating strain on a wafer. In particular, the invention relates to a method for fabricating strain on a silicon-on-insulator (SOI) wafer.
The mobility of the carriers in a device is directly related to the its current. The higher the current the faster the device is operated. Devices can be built as bulk devices, devices on silicon on insulator (SOI) or any other types. Each type has its own characteristics that make it attractive. As these devices are scaled down, one of the characteristics that may be of interest is the speed of metal oxide semiconductor (MOS) transistors. One way to make a speedier transistor is to create a thinner gate oxide and therefore create more capacitance, which results more charge. Another way is to create a high mobility channel.
To have a high mobility channel is to have high carriers mobility in the device. Straining the channel region of the MOS devices produces higher mobility of the carriers since tensile strained silicon causes increases in the mobility of both electrons and holes. Higher the mobility of these carriers means higher current; therefore faster devices or faster chips.
The method of growing strained silicon film on top of Silicon Germanium (SiGe) layer in bulk devices (e.g., silicon substrate) is standard and is well known in the art. Growing strained silicon film onto silicon-on-insulator wafer, however, is difficult since it would thicken the active silicon layer on the SOI beyond the range of useful interest.
A method of fabrication of a thin film strained silicon layer on an oxide substrate (i.e., thin body SOI) is described.